Manufacture of steel tubes from steel strip by electron bombardment

ABSTRACT

The invention relates to a process for the manufacture of steel tubes from steel strip by electron bombardment in vacuo. Vacuum is applied to one end of a tube, the other end being open. The welding operation taking place at the end adjacent the application of vacuum. A sleeve is provided inside the tube to ensure a sufficient degree of vacuum at the welding position.

wan-71 Gi l 3 9 5 96 9 946 United States Patent Inventors Jacques JeanLucien Valleins Paris; Bernard Max Eugene Begue, Pavilion-sous- Bois,both of, France Appl. No. 793,091

Filed Jan. 22, 1969 Patented July 27, 1971 Assignee Vallourec Usines aTubes de Lorraine- Escaut et Vallourec Reunies Paris, France PriorityJan. 23, 1968 Luxembourg 55,333

MANUFACTURE OF STEEL TUBES FROM STEEL STRIP BY ELECTRON BOMBARDMENT 9Claims, 4 Drawing Figs.

US. Cl 2l9/l2lLB Int. Cl 823k 15/00 FleldotSearch 219/121,

[561 References Cited UNITED STATES PATENTS 2 788,430 4/1957 Oakley219/60 3,169,182 2/1965 Oakley 219/60 3,440,390 4/1969 McCullough219/121 2,496,188 1/1950 Wiese 219/61 3,028,469 4/1962 Bognar 219/8.53,426,173 2/1969 Steigerwald 219/121 Primary Examiner.l. V. TruheAssistant ExaminerRobert ONeill AtwmeyBreitenfeld & Levine ABSTRACT: Theinvention relates to a process for the manufacture of steel tubes from.steel strip by electron bombardment in vacuo. Vacuum is applied to oneend of a tube, the other end being open. The welding operation takingplace at the end adjacent the application of vacuum. A sleeve isprovided inside the tube to ensure a sufficient degree of vacuum at thewelding position.

PATENTEU JULZT l9?! IHVENTOR Jnaqun a: 4. wuw'm:

A rrn m ll! MANUFACTURE OF STEEL TUBES FROM STEEL STRIP BY ELECTRONBOMBARDMENT This invention relates to the manufacture of tubes fromwelded steel, special steels or stainless steels in particular.

In a conventional type of installation, a roll of strip metal is as arule continuously unwound, and the strip passes through a formingstation which converts it into tube form, then through a welding stationfor welding the edges together and, finally, through a calibratingroller preceding a cutting unit which cuts the tube into predeterminedlengths.

Hitherto, welding has mainly been carried out by are welding in an inertatmosphere or ionizing atmosphere. In spite of the advantages of thisparticular technique, it has the disadvantage inter alia of restrictingthe rate of production or output.

The present invention relates to a means for welding the edges of thestrip metal together, by virtue of which it is possible to reach outputsconsiderably increased in relation to what has hitherto been possible,to obtain welds of outstanding quality even with metals that aredifficult to weld or for the manufacture of multiple-wall tubes withdifferent metals, to weld tubes of greater thickness and at the sametime to obtain products of the same quality as the tubes welded in theabsence of a supporting metal, and in certain cases, in particular forsmall tubes, to avoidthe operation of scraping or flattening the weldbead.

According to the invention, the technique of welding in a vacuum byelectron bombardment is applied to the continuous manufacture of metaltubes. This technique employs an electron gun which emits electronscapable of producing a weld providing the electron beam does not passthrough a zone in which an excessively high pressure prevails. Forexample, the vacuum between the gun and the working plane is generallykept between and 10 torr, a pressure in respect of which there is neverany need to use VHT (very high tension) and which accordingly does notcall for elaborate protection against X'rays.

Accordingly, it has hitherto only been possible to apply the techniqueof welding by electron bombardment to sections of limited length capableof being accommodated in an enclosure in which an adequate vacuum isgenerated.

Before the technique of vacuum welding by electron bombardment could beapplied to continuously delivered tubes, certain problems associatedwith the very nature of these products had to be solved.

First of all, applicants used to good effect a particular phenomenon fortaking into account that the sections to be welded are of almostinfinite length. It was found that if one of the ends of a tube isconnected to a vacuum pump, its other end being open to the atmosphere,a satisfactory vacuum can be set up in the vicinity of that endconnected to the pump providing the tube is long enough, there is noneed to provide a perfect seal at the open end of the tube.

However, in view of the very form of the tube, a perfect seal has to beprovided not only outside but also inside the tube. This is possibleproviding the edges of the strip of metal are prized apart beforeentering the welding station so as to accommodate inside the tube, inparticular below the welding station, means which provide for a certaindegree of tightness, on the lines of a seal, during the weldingoperation.

In addition, the very form of the tube prompted applicants to provide arefractory composition inside the tube where it is welded in order toprotect both the means which provide for a certain level of tightnessinside the tube, and also the lower surface of the tube against theelectron beam.

Accordingly, a station for welding a continuously delivered metal tubein vacuo by electron bombardment in accordance with the inventioncomprises an electron gun connected to a fluidtight housing capable ofaccommodating the sets of rollers required for guiding and welding thetube, being extended at each end by sleeves long enough for the vacuumobtained by at least one main pump connected in the vicinity of thewelding zone to be sufficient to permit welding, taking into account theadditional sealing means optionally provided at the free ends of thesleeves and/or partial vacuums generated in the sleeves, sealing meansbeing provided inside the tube above and below the welding station, andmeans being provided inside the tube to protect at least the lowersurface of the tube against the effect of the electron beams emitted bythe aforementioned electron gun.

It may be of advantage to provide means completing the pumping action ofthe vacuum pump connected to the housing along the sleeves and inparticular near the ends. These means may comprise on the one handmechanical, hydraulic or pneumatic sealing means in contact with thetube passing through the welding station, and on the other hand a slightvacuum generated for example by vane pumps connected to the spacebetween the moving tube and the sleeves.

The internal sealing means may comprise mechanical sealing means such ascylinders in a plastics material with a low coefiicient of friction,such as polytetraufluoroethylene. If a tool is provided for scraping orflattening the weld bead inside the tube, these sealing means are withadvantage carried by the rod used to support the aforementioned tool.

In this case, it is advisable to provide rollers by which the tube issuitably opened just before entering the welding station, and rollerswith means placing the edges in a correct position relative to theelectron beam, and finally rollers which reclose the tube just beforewelding and rollers holding the edges tightly against one another afterwelding. In this way, the sealing means may be supported inside the tubeby a support extending between the edges of the strip of metal prizedapart before entry into the welding station.

The means which protect the lower surface of the tube at leastpreferably consist of a piece of molybdenum, for example in the form ofa bar. Where a rod or similar support is arranged inside the tube, thisrod also has to be protected against the electron beam. To this end,part of the rod is with advantage made of a refractory material such asmolybdenum, or alternatively the rod is made with a nacelle toaccommodate the bar of molybdenum or similar material.

According to another aspect of the invention, the tube is preferablypreheated near the welding zone, as known per se for tubes of ordinarysteel and also for tubes of stainless steel welded in an inert orionizing atmosphere.

Various methods of preheating are possible. ln a first method, theelectron beam supplied by the gun to make the weld is deformed in such away that deformation of the spot ensures preheating of the edges. Anadditional gun may also be arranged above or upstream of the main gun.Finally, preheating may be carried out by medium frequency orradiofrequency induction.

Other features which also form part of the invention will be apparentfrom the following description in conjunction with the accompanyingdrawings given primarily by way of example in which:

FIG. 1 is a diagrammatic section through part of the production line onwhich a welded tube according to the invention is made,

FIG 2 diagrammatically illustrates the inside of a tube duringproduction, and

FIGS. 3A and 3B show modified embodiments of the means which protect theinner surface of the tube.

In FIG. I, the reference 1 denotes a strip of metal, deliveredcontinuously, which has already been converted by preceding stations(not shown) into a tube of circular cross section. A set of rollers 2combined with a fixed or displaceable blade 20 ensures that the tube issuitably opened as it enters the welding station so that the meanscapable of generating the required vacuum inside the tube can beintroduced into it.

The welding station comprises an electron gun generally denoted by thereference 2 which consists of a filament 3, a cathode 4, and anode 5with feed cables 6 for the filament and the cathode. Placed in the axisof the gun is a concentrating coil 7 connected to a suitable voltagesource.

The electron gun, in which the requisite vacuum is generated by means ofa pump (not shown) is connected to a tubular housing 8 designed toaccommodate a set of suitable rollers, being extended at either end bysleeves 9 and 10, respectively, of appreciable length, i.e. some meters.A vacuum pump 11 is connected to the housing 8 in the vicinity of thewelding zone.

The rollers accommodated in the housing 8 may comprise a first set 12cooperating with a blade 13 for placing the edges of the strip in acorrect position relative to the beam of electrons emitted by the gun2'. The first set of rollers is followed by a second set 14 by which thetube is closed just before welding, and by a set of pressure rollers 15holding the edges tightly against one anotherjust after welding.

In the vicinity of the free ends of the sleeves, a gentle vacuum ispreferably created between the sleeve and the tube by means of a pumpsuch as a vane pump l6, l7 sucking into annular chambers 18 and 19,respectively, provided for this purpose. In addition, mechanical means,hydraulic means or pneumatic means 20 and 21 in contact with the tubeseal off the ends of the sleeves.

In certain cases, it is of advantage to provide inside the tube a tool22 which is normally used to scrape or flatten the weld bead. This toolis carried by a bar or tubular element 23 which simultaneously acts as asupport for the internal sealing means 24 and 25.

If a tool of this kind is not absolutely essential, a correspondingsupport may be provided.

These sealing means are arranged in contact with the inner surface ofthe tube to complete the sealing action of the outer means 20 and 21.

The internal sealing means 24 arranged substantially opposite theexternal means 20 may with advantage consist of a cylinder in a plasticsmaterial, for example polytetrafluoroethylene, with a longitudinalgroove on the outside positioned on the upper part of the tube in such away that it partially obscures the opening provided by the blade 20.

The sealing means 25 which may be of considerable length may optionallybe improved in terms of efficiency by allowing a liquid of extremely lowvapor pressure to flow at a regular rate of flow on to the topdownstream end of these means through a small tube 26 incorporated inthe rod 23 or in the supporting rod or tube, in such a way that theliquid impregnates the entire inner surface of the tube.

It may also be of advantage to provide an additional pump maintaining apartial vacuum inside the tube. This vacuum may be created through therod 23 acting as a support for the internal sealing means and the tool,if any, used to scrape the weld bead.

It is advisable to provide a composition protecting both the lowersurface of the tube and the rod or tubular element 23 in the pathfollowed by the electron beam beneath the upper surface of the tube.This composition is a refractory composition, preferably molybdenum. Itmay be in the form of a bar 27 forming part of the rod 23 (FIG. 3A). Itis also possible to provide on the rod or tubular element 23 a nacelle28 in the thickness of which the molybdenum bar 29 is accommodated (FIG.33).

It may be of advantage to cool the protective composition by circulatingwater.

The tube is preferably preheated near the welding zone as known per sefor welding ordinary steel tubes and also for welding stainless steeltubes in an inert or ionizing atmosphere. In the example shown,preheating is effected by an additional electron gun 30 inclinedrelative to the axis of the main gun 2. It is also possible to use forthis purpose medium frequency or radiofrequency induction coils 31located before the gun 2' or in front of the blade 13. A screen 32 ispreferably provided to protect the electronic lenses against the effectsof RF.

Naturally, the production line for tubes welded in accordance with theinvention has to be modified in relation to a conventional productionline, not only by replacing the conventi nal welding station by anelectron bombardment welding station, but also by increasing thedistance separating the welding station from the forming station and thecalibrating station, respectively, so as to allow positioning of thelong sleeves connected to the housing of the welding station. Inaddition, the strip metal used should be clean and dry and in particularfree from oil to avoid any evaporation in the welding zone.

It is obvious that the embodiment described has been given above all byway of example and that it may be modified in several ways withoutdeparting from the scope of thc invcntion.

Thus, other pumps such as 16 and I7 may be provided in the vicinity ofthe housing 8, whilst two pumps such as 11 may be provided on eitherside of the axis of the electron gun 2. Similarly, it may be ofadvantage to provide chican in the sleeves 9, 10 in order to form kindsof compartments to each of which a pump is connected. Finally, toprovide a seal at 20, i.e. below the welding station, an annular pumpmay be arranged in such a way as to blow a liquid screen substantiallytangentially on to the tube in the direction in which it travels.

In addition, the pump 11 may be associated with an auxiliary regulatingpump 11' controlled from a pressostat l1 measuring the vacuum in thevicinity of the welding zone. This pump 11 completes the action of themain pump 11 so that the vacuum in the welding zone is constant whateverthe fluctuations in pressure attributable to production.

We claim:

I. A welding station for welding together the butting Iongitudinal edgesof a stripformed into a tube which moves continuously through thestation, comprising a housing having two spaced-apart ends,

means for creating a partial vacuum within said housing,

an electron gun connected to said housing for providing a beam capableof welding the tube material,

means within said housing for pressing the longitudinal edges of thetube together immediately before and after they are welded,

a relatively long sleeve extending from each end of said housing, theinterior of each sleeve communicating with the interior of said housing,

means for moving the tube longitudinally so that the tube enters saidhousing by passing through one sleeve and leaves said housing by passingthrough the other sleeve,

means near the end of each sleeve remote from said housing for aidingthe maintenance of a partial vacuum in said housing, said means near theend of each sleeve cooperating with the length of its respective sleeveto maintain the desired partial vacuum in said housing,

spaced-apart sealing means inside the tube, one of said sealing meansengaging the tube before it enters said housing and another of saidsealing means engaging the tube after it leaves said housing, and

protective means inside the tube in the region of said gun forprotecting the portion of the tube opposite the edges being welded fromthe effects of the beam provided by said gun.

2. A welding station as defined in claim 1 wherein said means near theend of each sleeve includes a seal engaging the interior of the sleeveand the exterior of the tube.

3. A welding station as defined in claim 1 wherein said means near theend of each sleeve includes means for creating a partial vacuum in thespace between the sleeve and the tube.

4. A welding station as defined in claim 1 wherein said sealing meansinside the tube each includes a plastic cylindrical element having a lowcoefficient of friction.

5. A welding station as defined in claim 1 including an elongated memberextending along the length of and inside the tube, a tool carried bysaid member for scraping the weld bead from said tube, said member alsocarrying said sealing means inside the tube.

6. A welding station as defined in claim 1 wherein said protective meansincludes a molybdenum bar.

7. A welding station as defined in claim 1 including an elongated memberextending along the length of and inside the tube, a tool carried bysaid member for scraping the weld bead from said tube, said member alsocarrying said protective means.

8. A welding station as defined in claim 1 in combination with means inadvance of the welding station for separating the longitudinal edges ofthe tube to open the latter, means in advance of said gun forpositioning the longitudinal edges of the tube with respect tothe beamfrom said gun, and means 1 member also carrying said sealing meansinside the tube and said protective means.

2. A welding station as defined in claim 1 wherein said means near the end of each sleeve includes a seal engaging the interior of the sleeve and the exterior of the tube.
 3. A welding station as defined in claim 1 wherein said means near the end of each sleeve includes means for creating a partial vacuum in the space between the sleeve and the tube.
 4. A welding station as defined in claim 1 wherein said sealing means inside the tube each includes a plastic cylindrical element having a low coefficient of friction.
 5. A welding station as defined in claim 1 including an elongated member extending along the length of and inside the tube, a tool carried by said member for scraping the weld bead from said tube, said member also carrying said sealing means inside the tube.
 6. A welding station as defined in claim 1 wherein said protective means includes a molybdenum bar.
 7. A welding station as defined in claim 1 including an elongated member extending along the length of and inside the tube, a tool carried by said member for scraping the weld bead from said tube, said member also carrying said protective means.
 8. A welding station as defined in claim 1 in combination with means in advance of the welding station for separating the longitudinal edges of the tube to open the latter, means in advance of said gun for positioning the longitudinal edges of the tube with respect to the beam from said gun, and means between said positioning means and said gun for closing the tube immediately prior to welding.
 9. A welding station as defined in claim 8 including an elongated member extending along the length of and inside the tube, said member entering the tube through the opening provided by said edge separating means, a tool carried by said member for scraping the weld bead from said tube, said member also carrying said sealing means inside the tube and said protective means. 